Integrated process for producing tert.butyl alkyl ethers and butene-1

Abstract

Tert.butyl alkyl ethers are produced from a C 4 hydrocarbon feedstock containing isobutene, and the butene-1 is recovered at high purity by extractive distillation of the isobutene-free C 4 hydrocarbon stream in the presence of a solvent chosen from acetone, acetonitrile, dimethylformamide, methanol, n-methylpyrrolidone, formylmorpholine and furfural. After removing the solvent, the extract is rectified, and the butene-1 separates as overhead product of high purity.

I claim: 
     
       1. An integrated process for producing tert-butyl alkyl ethers and butene- 1 from a C 4  hydrocarbon feedstock optionally containing C 3  and C 5  components and non-hydrocarbon components, the butadiene having been previously separated from said feedstock, comprising (a) feeding the C 4  hydrocarbon feedstock which is substantially free of butadiene to a tert-butyl alkyl ether synthesis section which is filled with a catalyst constituted by an acid ion exchange resin,   (b) reacting the isobutene contained in the C 4  hydrocarbon feedstock with an aliphatic alcohol in order to produce a tert-butyl alkyl ether,   (c) separating the tert-butyl alkyl ether from the residual C 4  hydrocarbons by distillation,   (d) subjecting the residual C 4  hydrocarbons to extractive distillation in the presence of a solvent in order to separate most of the C 4  saturated hydrocarbons and the lighter hydrocarbons (C 3 ) present as an overhead product from a bottom product which is an extract comprising the solvent, butene-1, butene-2, the remainder of the C 4  saturated hydrocarbons and the heavy hydrocarbons (C 5  +),   (e) then subjecting the extract to stripping in order to separate the solvent from the remainder of the extract,   (f) recycling the solvent to the extractive distillation,   (g) distilling the remainder of the extract to give an overhead fraction constituted by butene-1 and a bottom fraction comprising butene-2 and butene-1 and the balance of the extract,   (h) passing the bottom fraction through an isomerization stage in which the butene-2 and the unrecovered butene-1 are partly converted into isobutene to obtain an isomerized hydrocarbon fraction containing butene-1, butene-2 and isobutene,   (i) separating said isomerized hydrocarbon fraction from the remainder of the products, and   (j) feeding the isomerized hydrocarbon fraction containing butene-1, butene-2 and isobutene to the tert-butyl alkyl ether synthesis.   
     
     
       2. A process according to claim 1, wherein the extractive distillation is carried out in the presence of a solvent selected from the group consisting of acetone, acetonitrile, dimethylformamide, methanol, n-methyl pyrrolidone, formylmorpholine and furfural. 
     
     
       3. A process according to claim 1, in which said acid ion exchange resin in said tert-butyl alkyl synthesis section is of the sulphonated divinylbenzene-styrene type. 
     
     
       4. A process according to claim 1, in which in step (b) the molar ratio of aliphatic alcohol to isobutene is between 0.9 and 1.3. 
     
     
       5. A process according to claim 1, in which the C 4  hydrocarbon feedstock in step (a) has a butadiene content of less than 0.5% by weight.